Effectiveness of Zoledronic Acid in the Prevention of Osteoporosis in Early Breast Cancer Patients Receiving Letrozole

Inclusion Criteria: * Postmenopausal women with histologically documented early (non-metastatic) breast cancer * Previous treatment with tamoxifen for at least 2.5 years and not more than 3.5 years * Assigned to receive letrozole treatment * Karnofsky performance status ≥ 70 * Life expectancy ≥ 16 weeks * Signed informed consent after full explanation of study by participating clinician and prio to any study specific procedures * Adjuvant or neoadjuvant chemotherapy is allowed * No clinical and/or radiologic evidence of distant metastases * No prior treatment with an aromatase inhibitor * Able to comply with treatment and scheduled follow-up visits * Age between 18 and 82 years Exclusion Criteria: * Pregnant or lactating women or women with child bearing potential * Patients with other malignancies except except adequately treated basal cell carcinoma of the skin or in-situ cervix carcinoma * Active infection or other serious underlying medical condition which would impair the ability of the patient to receive protocol treatment * Clinical and/or radiological evidence of distant metastases. * Evidence of pathological fracture * Prior treatment with an aromatase inhibitor * Prior administration of any intravenous bisphosphonate during the last year. * Oral bisphosphonate must be discontinued within 4 weeks of enrollment * Administration of long-term systemic corticosteroids within the last 12 months (short term steroid treatment is allowed.) * Prior use of parathyroid hormone treatment for more than 1 week * Use of any drug known to affect the skeleton (calcitonin, mithramycin, gallium nitrate) within two weeks prior to enrollment * Abnormal renal function: creatinine clearance must be above 30 ml/min (calculated by Cockroft formula) * Evidence of metabolic bone disease( Paget's, osteogenesis imperfecta, hyperparathyroidism within the 12 months prior to enrollment) * Baseline lumbar spine and or total hip Bone Mineral Density T score below -2 * Known hypersensitivity to zoledronic acid * Psychological, familial, sociologic, or geographic conditions which do not permit medical follow-up and compliance with the study protocol * White blood cell ≤ 3.0 x 10exp9 /L or granulocytes ≤ 1.5 x 10exp9/L or platelets ≤100 x 10exp9 * Total bilirubin\> 1.5 x upper normal limit, SGOT and SGPT \> 2.5 x upper normal limit * Unable to undergo DXA bone density scanning (spine deformity, severe scoliosis, lumbar sacral spine surgery)